I am a fairly new member here and I have a 99' S-70 T-5. She's not doing so well as of the last few months.
It has several issues that I need some input on.
The car runs rough while idling. There is steady smoke coming out of the exhaust and if I hit the gas hard there is a massive black cloud that blows out of the exhaust. (I am not sure if this is related to that but recently and sometimes after I put the car in D or Reverse, the car sort of jerks into gear particularly while parallel parking and the brake pedal becomes very hard to push but returns to normal in neutral or park). The car is burning through gasoline light a rocket.
Also the check engine light is on with the the 02 sensor being the culprit P0134.
Do you think this is a matter of doing a once over on the PCV system?
Any opinions or useful information would be much appreciated.

 

Black smoke indicates a rich fuel mixture, which correlates with your high fuel consumption. Pull the plugs and examine them.

Replace the O2 sensor.

How bad is the idle? Is the car firing on all cylinders? Worst case scenario is a bad head.

But I think there's more to be fixed. The plugs are likely fouled. When was the last full tuneup (plugs, wires, filters, fluids, etc.) done? And if the PCV components haven't been done in a while, replace them as well.

Jerking when changing gears seems like motor mounts to me.